We plan to determine if photoperiod affects the number of pulsatile releases of luteinizing hormone in prepubertal heifers. Determination will be made of effects of Oh, 9-12 h, 16 h and constant light on body growth lactation and prolactin concentrations in sera of growing heifers and lactating cows. The effects of season on prolactin secretion in pinealectomized steers will be tested. The influence of a variety pineal substances will be tested for their abilities to release in prepubertal bulls and in bovine pituitary cells cultured in vitro.